Applications currently exist for enabling computer-to-computer telephony applications using a protocol know as Video Audio Tool or "VAT", which is a product of the Network Research group of Lawrence Berkeley National Laboratory. Particulars of the VAT protocol are well known in the art and are therefore not further described herein. Examples of such applications include "DigiPhone for Mac," available from Third Planet Publishing of Dallas, Tex., and designed for use with Macintosh computers, and "Internet Phone," available from Vocaltec of Northvale, N.J., and designed for use with IBM-compatible PCs. Typically, such communication between computers occurs over a wide area network ("WAN"), such as the Internet.
As described above, there are various applications for enabling telephonic communication between two computers; however, it will be recognized that there are many situations in which it would be useful to enable a computer to communicate directly with a telephone via a public switched telephone network ("PSTN"). For example, in a situation where a user has only a single telephone line, is using his computer to access the Internet and needs to make a telephone call to a third party who does not have computer or whose computer is not logged on to the Internet at the present time, it would be advantageous for the user to be able to call the third party's telephone from his or her computer via the Internet.
Presently, VAT-based TCP/IP telephony applications use signaling protocols designed exclusively for signaling on a computer network, such as the Internet. These signaling protocols are minimal and are inadequate to originate telephone call into a PSTN.
Because VAT is a telephony protocol designed to enable computer-to-computer telephony applications via a computer network, such as the Internet, it does not enable the originator of a call to send adequate information into the network to originate a call into a PSTN. At least some VAT applications do support a minimal text description of the caller to be included in the info field of the VAT ID message, which is the message VAT uses to originate a call. Accordingly, it would be possible for a system to be designed that requires the user to place the PSTN destination telephone number in the info field to originate a call to a PSTN endpoint. However, the amount and nature of the information that may be sent in this manner is limited. Furthermore, applications that implement the VAT signaling protocol typically do not enable a user to modify the info field, and, since this field is intended to be used to provide information about the originator, it is common for a vendor of the application to hard code the name of the registered user of the software into this field as a means of copy protection.
Accordingly, what is needed is a system for extending the use of a VAT TCP/IP telephony application to originate calls into a PSTN, as well as a computer network, by extending the VAT signaling protocol.